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Master Fader: Olet väärässä. Jos et usko minua, lue vaikka tämä artikkeli:
 
Juuh, kuten sanoin, mikäli kyseessä on *kaksi samalla filtteröintimetodilla toteutettua EQ:ta* (esim useimmat digi-eq:t ovat perus 2nd order biquad IIR-filttereitä joissa coefficienttien laskentametodi ja käyttöliittymä vaihtelee) niin EQ:t saa nullaamaan keskenään, eli vaihe- ja taajuusvasteet matchaavat toisiaan.
 
Kaikki digi-EQ:t eivät kuitenkaan ole IIR-pohjaisia, esim. linear phase eq:t on yleensä toteutettu FFT:llä / konvoluutiolla (mistä johtuen niissä vaihe pysyy halutessa suorana mutta impulssivaste vaihtelee).
 
Ja, niinkuin myös mainitsin, jotkut softa-eq:t käyttävät allpass-filttereitä (= "ylimääräisiä" filter passeja) tasoittamaan vaihevastetta, jolloin EQ:sta ulostuleva signaali on vaihevasteeltaan pelkkää perus 2nd order Biquad IIR:ää tasaisempi. Siksi ei voi yleistää että "Kaksi toiminnaltaan erilaista eq:ta, jotka tuottavat saman taajuusvasteen muutoksen, tuottavat saman vaihevasteen muutoksen" ;)
 
Samasta asiasta tässä kuitenkin puhutaan ;)
 
Typeräksi nenänkaivuuksihan tää menee, mutta luepas vaikka tää...
 
http://www.hydrogenaudio.org/forums/lofiversion/index.php/t73061.html
 
"As someone said, analog filters are minimum-phase, generally, although strictly speaking, elliptic filters create an "interesting" version of minimum-phase filters.
 
Digitally, for IIR filters, the poles must still be minimum-phase (i.e. stable... the two go together, minimum-phase and stability) but the zeros need not be minimum phase, in real zeros or zero pairs can be more or less any value.
 
So, for IIR filters, it is impossible to STRICTLY create a linear-phase (i.e. constant delay) filter. That would require unstable poles. Another way to put it is that in order to create the constant delay filter, you need a symmetric impulse response, and for an IIR that would reach to minus infinity. So it goes...
 
(( Aside here... A constant delay creates a system wherein phase = 2 pi f t, where t is the delay, f is frequency, and phase is the unwrapped linear phase component...))
 
For FIR filters (all-zero filters) there is no such rule. If the FIR is symmetric about the middle of the filter, it WILL be constant-delay, no iffs, ands, or buts. This means, by the way, that each zero pair (or real zero) with radius over 1 has a pair with the same phase and the inverse (1/r) radius.
 
For an IIR filter, you get what you get. You can add pole-zero pairs to pull the phase more closely to linear phase, but that's it. You can't get there. (you use allpass filters to change phase only, this means that the zeros are the inverse of the poles in the filter, so it has a phase shift but an amplitude response of 1, or at least flat.
 
Interestingly, this means that if you decompose any allpass filter into second order sections (recommended), the coefficients (for a gain of 1 filter) will be ( a z^2 + b z + 1)/(z^2 +bz +a), i.e. the coefficients of the numerator will be the reverse of the coefficients of the denominator. This actually holds true for any order, of course, for a pure allpass.
 
This means that you can indeed create NON-MINIMUM_PHASE filters that are IIR in a digital setting, you can simply reverse the order of the numerator coefficients, you get the same amplitude response, but more phase shift. (hence not being minimum-phase any more). If you decompose the filter into second-order sections, you can reverse the numerator of each section individually, or of each real pole/zero pair individually, and still get the same magnitude response (but a different phase response), so it is possible to create a variety of things digitally."